PSI-LHCI of Chlamydomonas reinhardtii: Increasing the absorption cross section without losing efficiency

Clothilde Le Quiniou, Lijin Tian, B. Drop, Emilie Wientjes, I.H.M. van Stokkum, Bart van Oort, R. Croce

Research output: Contribution to journalArticleAcademicpeer-review

33 Citations (Scopus)

Abstract

Photosystem I (PSI) is an essential component of photosynthetic membranes. Despite the high sequence and structural homologies, its absorption properties differ substantially in algae, plants and cyanobacteria. In particular it is characterized by the presence of low-energy chlorophylls (red forms), the number and the energy of which vary in different organisms. The PSI–LHCI (PSI–light harvesting complex I) complex of the green alga Chlamydomonas reinhardtii (C.r.) is significantly larger than that of plants, containing five additional light-harvesting complexes (together binding ≈ 65 chlorophylls), and contains red forms with higher energy than plants. To understand how these differences influence excitation energy transfer and trapping in the system, we studied two PSI–LHCI C.r. particles, differing in antenna size and red-form content, using time-resolved fluorescence and compared them to plant PSI–LHCI. The excited state kinetics in C.r. shows the same average lifetime (50 ps) as in plants suggesting that the effect of antenna enlargement is compensated by higher energy red forms. The system equilibrates very fast, indicating that all Lhcas are well-connected, despite their long distance to the core. The differences between C.r. PSI–LHCI with and without Lhca2 and Lhca9 show that these Lhcas bind red forms, although not the red-most. The red-most forms are in (or functionally close to) other Lhcas and slow down the trapping, but hardly affect the quantum efficiency, which remains as high as 97% even in a complex that contains 235 chlorophylls.
Original languageEnglish
Pages (from-to)458-467
JournalBiochimica et Biophysica Acta. B, Bioenergetics
Volume1847
Issue number4-5
DOIs
Publication statusPublished - May 2015

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